Computers include general purpose central processing units (CPUs) that are designed to execute a specific set of system instructions. A group of processors that have similar architecture or design specifications may be considered to be members of the same processor family. Examples of current processor families include the Motorola 680X0 processor family, manufactured by Motorola, Inc. of Phoenix, Ariz.; the Intel 80X86 processor family, manufactured by Intel Corporation of Sunnyvale, Calif.; and the PowerPC processor family, which is manufactured by Motorola, Inc. and used in computers manufactured by Apple Computer, Inc. of Cupertino, Calif. Although a group of processors may be in the same family because of their similar architecture and design considerations, processors may vary widely within a family according to their clock speed and other performance parameters.
Each family of microprocessors executes instructions that are unique to the processor family. The collective set of instructions that a processor or family of processors can execute is known as the processor's instruction set. As an example, the instruction set used by the Intel 80X86 processor family is incompatible with the instruction set used by the PowerPC processor family. The Intel 80X86 instruction set is based on the Complex Instruction Set Computer (CISC) format. The Motorola PowerPC instruction set is based on the Reduced Instruction Set Computer (RISC) format. CISC processors use a large number of instructions, some of which can perform rather complicated functions, but which require generally many clock cycles to execute. RISC processors use a smaller number of available instructions to perform a simpler set of functions that are executed at a much higher rate.
The uniqueness of the processor family among computer systems also typically results in incompatibility among the other elements of hardware architecture of the computer systems. A computer system manufactured with a processor from the Intel 80X86 processor family will have a hardware architecture that is different from the hardware architecture of a computer system manufactured with a processor from the PowerPC processor family. Because of the uniqueness of the processor instruction set and a computer system's hardware architecture, application software programs are typically written to run on a particular computer system running a particular operating system.
Processor Virtualization
Computer manufacturers want to maximize their market share by having more rather than fewer applications run on the microprocessor family associated with the computer manufacturers' product line. To expand the number of operating systems and application programs that can run on a computer system, a field of technology has developed in which a given computer having one type of CPU, called a host, will include an emulator program that allows the host computer to emulate the instructions of an unrelated type of CPU, called a guest. Thus, the host computer will execute an application that will cause one or more host instructions to be called in response to a given guest instruction. Thus the host computer can both run software design for its own hardware architecture and software written for computers having an unrelated hardware architecture. As a more specific example, a computer system manufactured by Apple Computer, for example, may run operating systems and program written for PC-based computer systems. It may also be possible to use an emulator program to operate concurrently on a single CPU multiple incompatible operating systems. In this arrangement, although each operating system is incompatible with the other, an emulator program can host one of the two operating systems, allowing the otherwise incompatible operating systems to run concurrently on the same computer system.
When a guest computer system is emulated on a host computer system, the guest computer system is said to be a “virtual machine” as the guest computer system only exists in the host computer system as a pure software representation of the operation of one specific hardware architecture. The terms emulator, virtual machine, and processor emulation are sometimes used interchangeably to denote the ability to mimic or emulate the hardware architecture of an entire computer system. As an example, the Virtual PC software created by Connectix Corporation of San Mateo, Calif. emulates an entire computer that includes an Intel 80X86 Pentium processor and various motherboard components and cards. The operation of these components is emulated in the virtual machine that is being run on the host machine. An emulator program executing on the operating system software and hardware architecture of the host computer, such as a computer system having a PowerPC processor, mimics the operation of the entire guest. computer system.
The emulator program acts as the interchange between the hardware architecture of the host machine and the instructions transmitted by the software running within the emulated environment. This emulated environment might be created by a virtual machine monitor (VMM) which is a software layer that runs directly above the hardware and which virtualizes all the resources of the machine by exposing interfaces that are the same as the hardware the VMM is virtualizing (which enables the VMM to go unnoticed by operating system layers running above it). In this configuration a host operating system (HOS) and a VMM may run side-by-side on the same physical hardware. Alternately, the emulator program may be the HOS itself running directly on the physical computer hardware and emulating another hardware configuration. In a specific implementation of this embodiment, the HOS software may specifically comprise one embodiment of a “hypervisor.”
A hypervisor is a control program that exists near the kernel level of a HOS and operates to allow one or more secondary operating systems, other than the HOS, to use the hardware of the computer system, including the physical processor(s) of the computer system. A hypervisor emulates the operating environment for the secondary operating system so that the secondary operating system believes that it is operating in its customary hardware and/or operating system environment and that it is in logical control of the computer system, even though it may in fact be operating in another hardware and/or operating system environment and that the HOS may be in logical control of the computer system. This is significant because many operating systems function such that the operating system must operate as though it is in exclusive logical control of the hardware of the computer system. Thus, for multiple operating systems to function simultaneously on a single computer system, the hypervisor of each operating system must function to mask the presence of the other operating systems such that each operating system functions as though it has exclusive control over the entire computer system.
For simplicity, processor virtualization programs, including but not limited to VMMs and hypervisors, are collectively referred to herein as “virtualizers.” Moreover, any aspect of the inventions disclosed herein in the context of a hypervisor are also presumed to be equally valid and disclosed for a VMM and other virtualizers and vice versa.
Intercepts and Monitors
As known and appreciated by those of skill in the art, a major function of a virtualizer (e.g., a hypervisor or VMM) is to intercept events that occur while software is executing on a guest operating system in a partition (an individual instance of a VM). In this context, an event is interaction that occurs between some component of the partition and some resource, physical or virtual, that is not in fact part of the partition. For example, a program executing in a first partition may want to send data to a certain peripheral device, where the operating system for that partition believes that it has exclusive control over said device. However, in this case, when the program sends its data through the guest operating system for its partition and the guest operating system attempts to communicate with the peripheral device, the virtualizer intercepts this communication and for managing this partitions access to said device along with other attempts by other partitions to do the same—that is, where the device is not in fact dedicated to any particular partition. By intercepting these kinds of events, the virtualizer essentially fools the guest OS into thinking that it owns all of the resources of the machine (like an OS executing on physical hardware typically does) when, in reality, the underlying physical resources are in fact being shared or partitioned among several virtual machine partitions. In this regard, the virtualizer is responsible for both intercepting such events and responding to the intercepts when they occur. Unfortunately, centralizing this kind of functionality in a single virtualizer operating outside of each partition requires the virtualizer to be quite complex when, for reasons readily apparent to skilled artisans, a more simple virtualizer is desirable. Therefore, what is needed in the art for a simpler virtualizer-intercept model that would still provide intercept functionality. The present invention provides one such solution.